Acquired SJB Assets and FDIC Loss Sharing Asset - Summary of PCI Loans by Internal Risk Ratings (Detail) (PCI Loans [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	$ 133,496	$ 173,104
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	26,706	38,961
Watch List [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	77,371	74,369
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	8,203	15,492
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	21,216	44,241
Doubtful & Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total PCI gross loans	$ 0	$ 41